A device for operating a hydrodynamic torque converter of a transmission device and a converter lock-up clutch corresponding to it, are known from DE 10 2006 006 179 A1, by means of which simply designed three-line converters can be operated without compromising driving comfort.
Furthermore, from DE 10 2006 006 180 A1 such a device is known, by means of which starting devices in the form of both two-line and three-line converters and lock-up clutches corresponding thereto can be operated, and which at least partially comprise a system-group-independent, standardized assembly.
Piston chambers of converter lock-up clutches associated with three-line converters are designed as closed pressure chambers with only one connection, both in the open and in the closed operating condition of the converter lock-up clutch. Accordingly these converter lock-up clutches also known as closed 3-line converter lock-up clutches as opposed to open 3-line converter lock-up clutches, in which the piston chambers of the converter lock-up clutches in the open operating condition of the converter lock-up clutches are in each case connected to a converter's inner chamber of the respectively associated torque converter, are characterized by greater seal complexity and thus higher manufacturing costs.
EP 1 918 082 A2 describes a device for actuating a frictional converter lock-up clutch of a hydrodynamic torque converter, designed as an open 3-line converter lock-up clutch, in which a piston of the converter lock-up clutch can be acted upon by a pressure of a converter's inner chamber that acts in the closing direction of the converter lock-up clutch and by a pressure of a piston chamber delimited by the piston that acts in the opening direction. At least in the open operating condition of the converter lock-up clutch the piston chamber is connected to the inner chamber of the converter, so the converter lock-up clutch is in the form of an inexpensively and simply designed open 3-line converter lock-up clutch. The inner chamber of the converter can be pressurized with hydraulic fluid via a first line. Hydraulic fluid can be discharged from the inner chamber of the converter via a second line. In addition the piston chamber of the converter lock-up clutch can be connected to a pressurized zone and to an essentially unpressurized zone.
For this purpose a control valve device is provided, by means of which in a first switching position the piston chamber of the converter lock-up clutch can be coupled directly to the pressure side of a hydraulic pump. The inner chamber of the converter is acted upon by a pressure set by a pressure-limiting valve positioned downstream from the pressure side of the hydraulic pump. Downstream from a return line of the hydrodynamic torque converter a further pressure-limiting valve is provided in the second line, by means of which a minimum pressure can be set in the converter's inner chamber of the hydrodynamic torque converter in order to avoid cavitation in the converter's inner chamber. In the first switching position of the valve device that supplies pressure to the piston space of the converter lock-up clutch, the pressure-limiting valve of the second line of the hydrodynamic torque converter is vented toward an unpressurized zone of the device.
In a second switching position of valve device the piston chamber of the converter lock-up clutch is vented by way of the valve device toward the unpressurized zone, so that when the valve device is switched to its second position the pressure in the piston chamber of the converter lock-up clutch falls abruptly to the pressure level of the unpressurized zone, which is usually essentially equal to zero or which corresponds to an ambient pressure around the device. At the same time, in a second switching position of the valve device the pressure-limiting valve in the second line is acted upon via the valve device by the pressure on the pressure side of the hydraulic pump as a pilot pressure.
Thus, in the second switching position of the valve device the pressure in the piston chamber falls abruptly, essentially to zero, and owing to the pressure acting in the inner chamber of the converter, which corresponds to the arithmetical mean of the inlet pressure and the outlet pressure of the hydrodynamic converter lock-up clutch set by the pressure-limiting valve, the converter lock-up clutch is changed abruptly to its closed operating condition in which a torque that depends on the actuating pressure effective in the converter's inner chamber can be transmitted by the converter lock-up clutch.
Thus the transmission capacity of the converter lock-up clutch also increases abruptly, but this impairs the driving comfort to an undesired extent. In addition the value of the transmission capacity of the converter lock-up clutch is abruptly increased by a further amount due to the application of the pressure on the pressure side of the hydraulic pump to the pressure-limiting valve in the second line, since in the second switching position of the control valve device the pilot pressure of the pressure side of the hydraulic pump additionally applied to the pressure-limiting valve in the second line leads to an increase of the counter-pressure in the converter upstream from the pressure-limiting valve in the second line, which increases the pressure in the converter's inner chamber that acts on the piston of the converter lock-up clutch in the closing direction.